Gun with rifiling and method of making the same



vlgma 3942- R. E. CARTER i 2,293,1l4

GUN WITH RIFLING AND METHOD OF MAKING THE SAME Filed Oct. 19, 1940 2 Sheets-Sheet 2 @g5 V W i J2 Z55/ if I 15 i? gru/umm Patented Aug. 18, 1942 star assaut:

GUN wim RIFLING ANDy Mnrnon or MAK- ING 'rnn- SAME;

The invention relates to guns with rifiing in the gun barrels, and more particularly to the form and characteristics of the rifiing, and methods of making the same.

In most guns in use prior to the present improvements, the rfling has included lands. alternating with grooves around the internal surfaces of the gun barrels. The lands and grooves have been twisted or spiralled longitudinally of the gun barrels, and the lands have had substantially straight sides when viewed in transverse cross-section, with sharp corners at the junctions of the sides With the lands and the groove bottoms.

It has long been known that such sharp cornered lands and grooves in the riiling of a gun barrel enhance fouling and make cleaning diicult, but certain other disadvantages of such rifling have been generally overlooked.

The shooting accuracy of a gun barrel with rifling, assuming a perfect bullet, depends upon a correct bore and groove diameter and a high finish of the rii'ling free from tool marks. It is very difficult to produce usual rifling with sharp cornered lands and grooves with a high nish free from tool marks.

The friction between the rifling and the bullet in sharp cornered riiiing is substantial. The greater the friction, the greaterthe breech pressure, and the less the velocity imparted to the bullet, and conversely.

Vibration is set up in any object, such as the barrel of a gun, which is subject to any shock, blow, or explosion. The greater thebreech pressure in a gun barrel, the greater the vibration, and conversely. Moreover, the form of the tubular cross-section of a gun barrel a'ects the character of the harmonics arising fromrvibration. It is believed that sharp cornered riiiing produces disruptive harmonics, and conversely.

Furthermore, a gun barrel with rifling accurately formed, free from tool marks, and having a high finish, retains its firing accuracy for a much greater time than usual gun barrels.

The accuracy and range, that is the trajectory, are determined by the reactions with the air of a bullet of any particular original- Weight and shape after leavingr the muzzle of a gun barrel with riing from which the bullet is fired by a given charge of powder. These air reactions are determined by the form and characteristics of the riiiing which reforms the bullet and imparts rotation to the bullet about its axis of forward motion.

'I'he sharp grooves formed in a bullet by the usual sharp cornered lands and grooves of usual rifiing produce a retarding action as the bullet rotates or spins in the air, similar to the action of a nat propeller in water. In military rifles,

for example, bullet speeds of 2800 feet per second are common and produce a bullet rotation of 168,000 R. P. M. whenthe riiiing twist is one per foot. From the principles of aerodynamics, it is apparent that sharp projections, however small, should be eliminated from the periphery of the bullet.

In the jacketed or metal-clad bullets now in common use, splitting of the jackets by the sharp cornered lands of usual rifling is frequent. In

'extra high velocity loads, this splitting starts disintegration of the bullets, and some fail to arrive'at the targets.

In the past some eiiorts have been made to produce riing without sharp corners, with limited success.

In no case prior to the present improvements, whatever the type of riflng, as far as is known to the present inventor, has it been possible to produce a gun barrel with rifling which can be formed by methods enabling extreme accuracy, and the grooves of which can be final finished to enhance the accuracy and at the same time to provide a high finish free from tool marks.

The objects of the present invention include the provision of a gun including a gun barrel with improved rifling free from sharp corners, thereby overcoming the above indicated disadvantages of sharp cornered riing.

Further objects of the present invention include the provision of a gun including a gun barrel with improved riing, preferably free from sharp corners, and adapted to be formed with extreme accuracy and with a finish free from tool marks, thereby attaining the above indicated advantages of an accurate, highly finished rifling.

Further objects of the present invention include the provision of a gun including a gun barrel having a rifling which is of such shape as to permit its being formed by accurate machining methods not hitherto available in riled gun barrel manufacture, including broaching.

Further objects of the present invention include the provision of a gun including a gun barrel having a riiiing which is of such shape as to permit iinal finishing by methods not hitherto available in rifled gun. barrel manufacture, including either grinding or burnishing or both.

Further objects of the present invention include the provision of improved methods of forming and nishing rif-ling in a gun barrel to produce an accurate, highly finished rifling, free from tool marks.

The foregoing and other objects are attained by the gun manufactures including guns, gun parts, combinati-ons, and sub-combinations, and the methods and method steps of making the same, which comprise the present inventicn, and

the natures of which are set forth in the following general statement, and preferred embodiments of which gun manufactures together with their mode of use are set forth by way of example in the following description together with preferred details of the methods and method steps of making the same, and which are par-V ticularly and distinctly pointed out and set forth in the appended claims forming part hereof.

The nature of the improved gun manufactures of the present invention may be stated in general terms as including in a gun, a gun barrel having an internal riiied tubular surface formed by side by side grooves merging at their sides with each other in ridges.

In transverse cross section perpendicular to the longitudinal axis of the rifled tubular surface, each groove comprises a curve preferably a circular arc tangentA to an outer circle and having extremities terminating in adjacent ridges and in an inner circle passing through Vthe ridges.

The radius of the circular arc is less than the radii of the outer circle and ofthe inner circle, the center of each circular arcbeing eccentric with the outer and inner circles, which are concentric with each other.

The diameter of the inner circle is preferably substantially equal to the caliber of the projectile fired by the gun.

Each ridge may have a width in an arc of Ythe inner circle of 0.002 inch as an upper'limiigin order to attain the desired diameter of the inner circle.

The improved gun manufactures are adapted for being made by the improved methods and method steps of the presentinvention, Vwhich may 'be stated in general terms as making a ried tube for a gun barrel and the like by forming in the internal tubularsurface of the tube side by side grooves merging at their ridges, preferably by removing material from inner portions of the tube preferably by broaching or grinding, or by broaching and grinding, followed preferably by ball burnishing the grooves.

By way of example, embodimentsV of the improved gun manufactures of the present invention, and diagrammatic views illustrating details of the improved methods and method steps of making the same, are illustrated in the accompanying drawings forming part hereof, in

which- Y Y Figure 1 is a side elevation of a .30 caliber military rifle as one -example of a gun which ma include the present improvements; Y

Fig. 2, an enlargedY diagrammatic fragmentary transverse sectional view illustrating the improved .30YcaliberV barrel of the rie of Fig. 1 as on line 2 2, Fig. 3; Y

Fig. 3, a fragmentary longitudinal sectional view thereof, as on line 3-3, Fig..2; Y

Fig. 4, a fragmentary sectional view showing one ofthe ridges of the improved riing extending in transverse cross section in an arc of the inner circle containing the ridges;

Fig. 5, an end elevation view of a broach cutter adapted for broaching the grooves and ridges in the internal tubular surface of al tube to form the improved rifling;

Fig. 6, an end elevation of Ya rotary cutting head adapted to cut one of the improved grooves in a tube, and to be indexed to cut the successive grooves in the tube;

Fig. '7, an end elevation illustrating a grinding tool adapted for successively grinding the improved rifling grooves in a tube; and

Fig. 8, an end elevation showing a ball burnishing tool adapted for ball burnishing one of the improved rifling grooves in a riiied tube.

Similar numerals refer to similar throughout the several views.

The military rie indicated generally by IB in Fig. 1 includes an improved gun barrel indicated generally by II, which together with other usual parts of a military rifle, such as a U. S. rifle, MI, comprise one embodiment of the present improvements in a complete gun.

The advantages of the improved gun barrel II, arise from the incorporation of the barrel II with the other usual parts of the gun or riiie Il] in ring a usual projectile, such as the bullet of a usual .30 caliber military cartridge.

The improved gun barrel or tube I I has formed in its internal tubular surface, usually through the entire length thereof, improved rifling including side by side grooves I2 merging at their sides with each other in ridges I3.

As shown in Fig. 3, the grooves and ridges are twisted about the longitudinal axis I4 of the rifle barrel I I and its internal tubular surface with the present improved rifling formed therein.

In transverse cross section perpendicular to the longitudinal axis of the rifled internal tubular surface as shown in Fig. 2, each groove comprises a curve I 5 preferably a circular arc tangent to an outer circle indicated by the dot-dash line IS and having extremities terminating in adjacent ridges I3 and in an inner circle passing through the ridges I3 and indicated by the dotdash line I1.

As indicated in the diagrammatic Fig. 2, the radius r of each circular arc I5 is less than the radius R of the outer circle I6 and also less than the radius R of the inner circle I'I.

The outer and inner circles I6 and I'I are concentric with each other, their common center lying in the longitudinal axis I4 of the gun barrel As shown in the diagrammatic Fig. 2, the center I8 of each circular arc I5 preferably lies in a bisecting radius indicated by the dot-dash line I9 of the angle included between the dot-dash radius lines 20 and 2| extending from the center of the concentric circles I6 and I'I in the longitudinal axis I4 of the gun barrel II through the extremities of the circular are I5 in adjacent ridges I3. Y

In the .30 caliber rifle I0 as above stated, the gun barrel Ilis intended for use with .30 caliber ammunition, and Vin any transverse cross section as shown in Fig. 2, the diameter of the inner circle I'I in which the ridges I3 lie is preferably substantially equal to the caliber of the projectile fired from the gun barrel I I.

In diagrammatic Fig. 2, values of the several radii R, R and 1 are indicated for the .30 caliber barrel, which is shown as having five grooves I2 and verridges I3, said values for the several radii being as follows:

R=0.154 R=0.150" t0 0.1501 720.1354 t0 0.1359

By thus providing the above set forth rifled internal tubular surface for the gun barrel I I, with grooves I2 and ridges I3, it is possible to form the grooves I2 and ridges I3 by the improvide methods hereof which may include removing material from internal portions of a tube as by broaching by a broach cutter or tool 22 illustrated in Fig. 5, the broach cutter being parts the tube in which the grooves I2 and ridges I3` formed with a plurality of cutting edges23 each extending transversely of and at one side of the longitudinal axis of movement 2A of the breach, each cutting edge 23 having a projection on a plane perpendicular to the axis which comprises a curve preferably as shown a circular arc tangent to an outer circle 25 and having extremities terminating in junctions 26 with extremities of the projections of adjacent cutting edges 23 in an inner circle 2'I concentric with the outer circle.

In using the broach cutter 22 it is inserted in the usual manner of breaching within the internal tubular opening of a tube, and the material is removed from the inner portions of the tube by effecting relative movement of the tool and the tube along the axis 24 with the cutting edges 23 cutting into the inner portions of the tube.

The axis 24 of the broach thus coincides with the longitudinal axis of the particular gun barrel ried by the broach, which is the longitudinal axis I4 of the gun barrel Il, and in which the cutting edges 23 form the grooves I2 and the ridges I3.

It is also possible to initially form each groove I2 as by the use of a rotary cutting head 28 shown in Fig. 6 whose radius coincides with the radius of the groove circular arc, and then by indexing the rotary cutting head 28 to cut the successive grooves in the tube.

Similarly the grooves I2 may be initially formed by a rotary rough grinding wheel whose radius is equal to the radius of the circular arc of the groove to be formed thereby.

However the grooves may be initially formed, they are adapted for being final finished by a grinding disk wheel 29 shown in Fig. '7, so that the completed gun barrel has a high finish on the grooves of its rifling entirely free from tool marks.

Either with or Without preceding grinding operations, the improved rifling in the gun barrel may be provided with a high finish by burnishing as by a ball burnishing tool 30 illustrated in Fig. 8.

For a .27 caliber barrel provided with the improved rifled internal tubular surface, six grooves and six ridges may be formed, and the radii of the several circles and circular arcs of the transverse cross section of the barrel at right angles to the longitudinal axis, corresponding to the similar radii of the .30 caliber barrel II, may be as follows:

In order to make the radius R of the inner circle of any particular caliber barrel provided with the present improvements substantially equal to the caliber of the projectile red in the barrel, each ridge may have a Width in an arc of the inner circle of 0.002 as an upper limit, as shown in Fig. 4.

For a .25 caliber barrel including the present improvements, six grooves and six ridges may be provided, and the several radii of the transverse cross section of the barrel perpendicular to the longitudinal axis, corresponding to the similar radii for the .30 caliber barrel II may be as follows:

R=0.1285" R'- -0.125 r=0.1063 to 0.1066

In making one of the improved gun barrels Il,

are formed, may itself'be produced by any desired method, one of the most usual of which is to bore a cylindric internal tubular surface in a shaft of suitable metal for the gun barrel, and the diameter of which is substantially that of the inner circle I1 in any transverse cross section of the gun barrel at right angles to its longitudinal axis.

In certain cases the initial tube may be produced by seamless tube manufacturing methods, or by the various methods of making build-up gun barrels.

In the improved gun barrel I'I the ridges I3 thus lie in a cylindric bore, the diameter R' of which thus constitutes the caliber of the barrel.

In the improved gun barrel II of the present invention, its novel internal rifled tubular surface is not formed as above set forth entirely by boring operations, which strictly speaking implies the penetration of a body as by turning an augur, gimlet, drill, or the like, against the body, although in some cases the internal tubular surface of a gun barrel is spoken of as its bore regardless of the transverse cross section thereof.

The production of the twist or spiral in the grooves I2 and ridges I3 of the improved gun barrel I I, may be effected by the usual method of producing relative rotation about the longitudinal axis I4 of the gun barrel II between the barrel II and whatever groove forming or finishing tool is being used, simultaneously with the relative longitudinal movement of the barrel and tool as material is being removed from the internal tubular surface of the barrel or tube by cutting or by grinding, or as the preferred burnishing of the already'formed grooves I2 is being carried out.

Burnishing the grooves provides the most advantageous finish for the improved rifling because similar to cold rolling sheets it creates on the grooves unmarked surfaces or glazed skins within the desired exceedingly close limits. Providing the final finish by grinding nevertheless produces a very superior rifling.

Another method of producing the twist in the grooves I2 and ridges I3 of the improved barrel II is to initially form the grooves and ridges longitudinally straight through the barrel or tube, and then to twist the tube itself about its longitudinal axis preferably before final finishing the grooves and ridges.

The improved gun manufactures as above set forth not only enables the attainment of a high shooting accuracy and long life of the barrel and a high accuracy of the bullet or projectile fired by the barrel through the attainment of the objects of the invention above set forth, but also enables the production of the improved gun barrels by the improved methods set forth herein.

The embodiments of the gun manufactures and the details of the method steps of the present invention illustrated and described herein are by way of example and the scope of the present invention is not limited to the same or to the particular details thereof, but is commensurate with any and all novel subject matter contained herein Which may at any time properly under the United States patent laws be set forth in the claims hereof or originating herein, and the elements of such claims are intended to include their functional or structural equivalents.

I claim:

1. The method of making a riiied tube for a gun barrel and the like, including forming in the internal tubular surface of the tube side by side grooves merging at their sides in ridges by re'- moving material from the inner portions of the tube until in transverse cross-section the ridges lie in an inner circle and each groove comprises a curve tangent to an outer circle and having extremities terminating in the ridges and then burnishing each groove by a rotary member having a curve corresponding to the groove curve.

2. The method of making a ried tube for a gun barrel and the like, including forming in the 10 gun barrel and the like, including forming in the 15 internal tubular surface of the tube side by side grooves merging at their sides in ridges by removing material from the inner portions of the tube until in transverse cross section the ridges lie in an inner circle and each groove comprises a circular arc tangent to an outer circle and having extermities terminating in adjacent ridges, and then iball burnishing the grooves.

4. The method of making a rifled tube for a gun barrel and the like, including forming in the internal tubular surface of the tube side by side grooves merging at their sides in ridges by broaching material from inner portions of the tube, and then burnishing the entire surfaces of the grooves.

5. The method of making a rifled tube for a gun barrel and the like, including forming in the internal tubular surface of the tube side by side grooves merging at their sides in ridges by grinding inner portions of the tube, and then burnishing the entire surfaces of the grooves.

ROY E. CARTER. 

